1. Field of the Invention
The present invention relates generally to an apparatus and a method for retransmitting data in a wireless communication system, and more particularly, to an apparatus and a method for operating an Automatic Repeat reQuest (ARQ) using operation state information of a Hybrid Automatic Repeat reQuest (HARQ).
2. Description of the Related Art
In a wireless communication system, an error may be generated for transmission data depending on a channel state of a radio resource that transmits data. In this case, the wireless communication system performs control and recovery on a data error using an ARQ technique in order to raise transmission reliability.
When using the ARQ technique, a reception end informs a transmission end of whether data received from the transmission end is successfully received. For example, when an error is not generated for data received from the transmission end, the reception end transmits ACKnowledge (ACK) information to the transmission end. In contrast, when an error is generated for data received from the transmission end, the reception end transmits Negative ACK (NACK) information to the transmission end.
The transmission end retransmits data depending on the ACK/NACK information received from the reception end. For example, when receiving ACK information from the reception end, the transmission end recognizes that the reception end has successfully received data. Accordingly, the transmission end transmits new data to the reception end. In contrast, after receiving NACK information from the reception end, the transmission end recognizes that an error has been generated for data corresponding to the NACK information. Accordingly, the transmission end retransmits original data of the data corresponding to the NACK information to the reception end.
A wireless communication system may additionally use HARQ to perform high speed data transmission. For example, the reception end may perform high speed data transmission by performing, at a HARQ module, retransmission before an ARQ module requests retransmission.
FIG. 1 illustrates a conventional procedure for transmitting data in a wireless communication system.
As illustrated in FIG. 1, a transmission end 100 transmits data 1 to a reception end 110 via an ARQ module 102 and a HARQ module 104 in steps 121 and 123.
A HARQ module 112 of the reception end 110 determines whether an error is generated for the data 1. If an error is generated for the data 1, the HARQ module 112 transmits HARQ NACK information for the data 1 to the HARQ module 104 of the transmission end 100.
In contrast, when an error is not generated for the data 1, the HARQ module 112 transmits HARQ ACK information for the data 1 to the HARQ module 104 of the transmission end 100 in step 125. In addition, the HARQ module 112 transmits the data 1 to an ARQ module 114 in step 127.
The transmission end 100 transmits data 2 to the reception end 110 via the ARQ module 102 and the HARQ module 104 in steps 129 and 131.
The HARQ module 112 of the reception end 110 determines whether an error is generated for the data 2. If an error is generated for the data 2, the HARQ module 112 transmits HARQ NACK information for the data 2 to the HARQ module 104.
However, if an error is not generated for the data 2, the HARQ module 112 transmits HARQ ACK information for the data 2 to the HARQ module 104 of the transmission end 100 in step 133. In addition, the HARQ module 112 transmits the data 2 to the ARQ module 114 in step 135.
The transmission end 100 transmits data 3 to the reception end 110 via the ARQ module 102 and the HARQ module 104 in steps 137 and 139.
The HARQ module 112 of the reception end 110 determines whether an error is generated for the data 3. If an error is generated for the data 3, the HARQ module 112 transmits HARQ NACK information for the data 3 to the HARQ module 104 in step 141.
The HARQ module 104 of the transmission end 100 retransmits the data 3 to the HARQ module 112 of the reception end 110 depending on the HARQ NACK information for the data 3 in step 143.
The HARQ module 112 of the reception end 110 determines whether an error is generated for the retransmitted data 3. If an error is generated for the retransmitted data 3, the HARQ module 112 transmits HARQ NACK information for the retransmitted data 3 to the HARQ module 104 of the transmission end 100 in step 145.
The HARQ module 104 of the transmission end 100 and the HARQ module 112 of the reception end 110 perform retransmission of the data 3 until the HARQ module 112 of the reception end 110 receives the data 3 without an error in steps 147 to 155. However, the HARQ modules 104 and 112 perform retransmission of the relevant data by only a predetermined number of times.
The HARQ module 112 of the reception end 110 determines whether an error is generated for the retransmitted data 3. If an error is not generated to the data 3, the HARQ module 112 transmits HARQ ACK information for the data 3 to the HARQ module 104 of the transmission end 100 in step 157. In addition, the HARQ module 112 transmits the data 3 to the ARQ module 114 in step 159.
As described above, a wireless communication system may provide a high speed data service through a fast retransmission request using the HARQ technique. However, when a radio channel state deteriorates and retransmission of a HARQ frequently occurs, the ARQ module 114 of the reception end 110 may doubly receive data.
For example, as illustrated in FIG. 1, the ARQ module 114 of the reception end 110 receives data 3 through HARQ retransmission in step 159. However, when an ARQ timer of the ARQ module 114 expires while the HARQ module 104 and the HARQ module 112 perform retransmission of data 3 in step 151, the ARQ module 114 transmits ARQ NACK information for the data 3 to the ARQ module 102 of the transmission end 100 in step 153. Consequently, the ARQ module 102 of the transmission end 100 retransmits the data 3 to the HARQ module 104 based on ARQ NACK information for the data 3 in step 161. The HARQ module 104 recognizes the data 3 provided from the ARQ module 102 as data 4 to transmit the same to the reception end 110 in step 163.
The HARQ module 112 of the reception end 110 determines whether an error is generated to the data 3 provided from the HARQ module 104. If an error is not generated to the data 3, the HARQ module 112 transmits HARQ ACK information for the data 3 to the HARQ module 104 of the transmission end 100 in step 165. In addition, the HARQ module 112 transmits the data 3 to the ARQ module 114 in step 167.
As described above, the ARQ module 114 of the reception end 110 unnecessarily receives the data 3 twice, through the HARQ retransmission and the ARQ retransmission, deteriorating throughput and wasting resources.